Steps to Get a Connection With an Online Mobile Phone

By: Ian Ball

?Step I: A call is received for a mobile phone by MTSO and is relayed to all base stations (BS) connected to it.
?Step II: The BSs send out a paging signal in their respective bands seeking an acknowledgement from the called mobile phone.
?Step III: The called mobile phone recognizes its number ih the cell in which it is currently located and sends an acknowledgement to the BS of the cell. BS in turn sends this information to MTSO .MTSO establishes connection of this BS with the fixed phone via PSTN. It also allocates a free channel to BS to communicate with the mobile phone. Connection is established between fixed phone and mobile via MTSO and BS.
?Step IV: If the mobile phone moves away from the cell whose BS established the connection, it picks up a new signal from the BS into whose domain it has shifted. This BS now allocates a channel to the mobile phone and connects it to MTSO. This is called handoff from one BS to another.
The above said procedure is for call from fixed to a mobile phone.


Mobile to fixed line
If an online mobile phone
wants to call a fixed line phone it establishes connection with the BS whose signal is the strongest and connects it to MTSO via this BS. MTSO assigns a channel after it finds that the fixed phone is free to receive a call. Now call can proceed. Handoff is the same as in step IV above.
The steps followed for calls from a mobile phone to another mobile phone are as follows:
?Step I: A mobile phone wanting to call is turned on and senses wireless signals available on various frequencies and picks the one which is strongest. It then selects the BS sending this frequency as its base.
?Step II: BS forwards the called mobile number to MTSO .MTSO relays this to all the BSs. BSs in turn send paging signals in their respective bands seeking an acknowledgement from the called mobile number.
?Step III: If the called mobile number is ON it picks up the paging signal and sends acknowledgement to the BS in whose cell it is currently located.
?Step IV: BS sends this information to MTSO which connects the BSs of the two mobiles so that conversation can proceed. If no acknowledgement is received by the BS due to called mobile being switched off or busy or out of range, this information is sent to MTSO which relays this information to the calling mobile via its BS.
?Step V: If any or both of the mobile phones move from current cell a procedure similar to that described in step IV of fixed to mobile phone is followed. All the above mentioned steps take place fast and once a connection is established it is maintained regardless of movement of the mobile phone and without any obvious disruption of the ongoing conversation.
In the above description only audio communication has been considered. Cellular communication system used nowadays namely GSM and CDMA are both digital systems and thus all the steps described also hold for digital communication.

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